Extensive investigations have been undertaken over many years to find materials that will be biologically and chemically stable towards body fluids. This area of research has become increasingly important with the development of various objects and articles which can be in permanent contact with blood or other fluids, such as artificial organs, vascular grafts, probes, cannulas, catheters and the like.
Among polymer materials described and used in biomedical field mention can be made notably of polystyrenes, polyethylenes, polytetrafluoroethylenes, polyurethanes, polyurethanes-ureas, siliconic-polyurethanes, polyacrylates.
All these materials for being used for manufacturing medical implants shall guarantee some fundamental requirements, such as notably:                absence of loss or release of soluble members in the living systems (e.g. in the physiological liquids), unless said release is intentional (e.g. controlled release of drugs);        stability in the living environment with no polymer degradation (e.g. no breach of the polymer chain, no crosslinking, hydrolysis, swelling which can impair mechanical properties of the implant);        mechanical and physical properties of the materials appropriated for the target function of the medical implant;        biocompatibility, no thrombogenicity, no cytotoxicity;        stability against sterilizing conditions.        
Currently available biomaterials comply with selected but not with all above mentioned requirements.
It is also known that the introduction of fluorinated segments in the polymer material of the medical implant can bring valuable advantages, increasing, for instance, the stability of said material.
For instance, it has been disclosed that the presence of a fluoroalkyl group increases the stability of a poly(trifluoropropyl)methylsiloxane, polymer used for biomedical applications (Non Patent Citation 0001: RATNER, Buddy D. Comprehensive Polymer Science. AGGARWAL, Sundar L. Ohio (USA): Pergamon Press, 1989. p. Vol. 7, Ch. 7, p. 228.).
Polytetrafluoroethylene (PTFE) has been proposed in the past for biomedical applications, thanks to its outstanding inertness, biocompatibility, stability, thus avoiding any risk of chemicals release due to polymer chain degradation. However, provided the non melt-processable nature and the intrinsic stiffness of PTFE, this material is not suitable for providing small diameter blood vessels prostheses or other cardiocirculatory devices which shall have an elastic behaviour similar to that of body circulatory system.
Polymer materials manufactured from fluoropolyoxyalkene compounds have been described in the art for biomedical applications.    Patent Citation 0001: U.S. Pat. No. 5,026,814 (AUSIMONT S.R.L.). Jun. 25, 1991. discloses fluorinated polyurethanes block copolymers, comprising rubber-like blocks consisting of polyoxyperfluoroalkylene chains and rigid blocks comprising short chain hydrogenated or fluorinated aliphatic moieties, said polyurethane being prepared from perfluoropolyethers comprising hydroxyl groups and being suitable for use in the biomedical sector, for the manufacture of artificial organs, artificial blood vessels, membranes, structural materials and the like.    Patent Citation 0002: U.S. Pat. No. 5,043,410 (AUSIMONT S.R.L.). Aug. 27, 1991. discloses fluorinated polyurethane block copolymers, comprising rubber-like blocks consisting of fluorooxyalkylene units and stiff blocks comprising olefinic unsaturation suitable for crosslinking, said polyurethane being prepared from perfluoropolyethers bearing hydroxyl groups and being appropriate for use in the biomedical sector for the manufacture of artificial organs, artificial blood vessels and membranes.
In vitro biocompatibility of fluorinated polyurethane has been also investigated; fluorinated polyurethane prepared from, inter alia, perfluoropolyethers bearing hydroxyl groups, have been shown to be non thrombogenic and non cytotoxic (Non Patent Citation 0002: SBARBATI DEL GUERRA, R. In vitro biocompatibility of fluorinated polyurethanes. Journal of Materials Science: Materials in Medicine, 1994 vol. 5, p. 452-456.).    Patent Citation 0003: U.S. Pat. No. 5,109,103 (AUSIMONT S.P.A.). Apr. 28, 1992. discloses a process for manufacturing polyesters comprising polyoxyfluoroalkylene blocks by polycondensation of perfluoropolyethers bearing hydroxyl groups with dicarboxylic acids or derivatives thereof, said polyesters being endowed with biocompatibility.
Nevertheless, the Applicant has found that said materials, when used in biomedical applications, might undergo chemical extraction phenomena by body fluids and release phenomena of low molecular weight fluorinated materials might impair their biocompatibility.
There is still a need in the art for a process for the manufacture of a medical implant, yielding biocompatible parts which are non thrombogenic, non citotoxic, and have suitable mechanical properties and which, in addition, do not undergo release of fluorochemicals when contacted with body fluids.
Also, are known in the art fluorinated thermoplastic elastomers obtainable by utilizing perfluoropolyoxyalkylene diols having a functionality of at least 1.97. Thus, Patent Citation 0004: U.S. Pat. No. 5,476,910 (AUSIMONT S.P.A.). Dec. 19, 1995. discloses thermoplastic polyester block copolymers obtained reacting a perfluoropolyoxyalkylene diol with a functionality at least equal to 1.97;    Patent Citation 0005: U.S. Pat. No. 5,508,380 (AUSIMONT S.P.A.). Apr. 16, 1996. discloses fluorinated thermoplastic elastomeric polymers obtained from polycondensation reactions of suitable condensation monomers, comprising, inter alia, perfluoropolyether reactive materials, having an average functionality of at least 1.97. Said materials have not been suggested for the manufacture of medical prostheses.